(i) Field of the Invention
The invention relates to a process for ducting or routing flue gases produced in the firing space of a boiler, in the case of which the flue gases within the boiler and giving up heat are run through heat absorbers themselves cooled by heat transport material and run to an off-gas stack; the invention is furthermore with respect to apparatus for undertaking this process for ducting or flowing flue gas.
(ii) The prior art
In the case of old heat producers (steam producers on the one hand and hot or warm water producers on the other) there has been a suggestion to make use of multi-pass heat producers, and more specially three-pass producers (see for example the German Industrial Standards (DIN) 4751, 4752 and the like). In the case of such old heat producers the multi-pass design made possible a generally high level of use of the heat development in the firing space.
In the case of a great number of process as used in industry, as for example thermo-chemical processes, heating systems for dryers in the wood and surface coating industries, for stretching or tenter frames in the textile industries, and dryers in the petroleum industry, it has, however, turned out to be necessary to make use of flue gases for direct or indirect heating in a temperature range between about 500.degree. C. and 900.degree. C. For such purposes the flue gases coming from normal heat producing plant, may not be used, because their temperature level (up to about 300.degree. C.) is far under the desired figure. So it has so far been necessary to make use of direct burner systems for such processes, in the case of which the flue gases produced in the firing space and having a high temperature, are lowered to the desired temperature by mixing in fresh air or by using only a part of the flue gases produced. In the two cases a markedly great amount of the radiation heat, produced in the firing space, and, in part, furthermore of the convection heat produced in the plant, was wasted so that the efficiency of such a plant under the desired level.